My first UV filter was a Steripen Adventurer. I liked it for its convenience, weight, and size, but it had some major problems. Once I was backpacking with a group, and let someone use it. I told him it was a UV lamp, and so if it were to come on out of water for some reason, don't stare at it. As things go, he asked me if the thing was working, and when I turned around, I saw he had it out of the Nalgene bottle and it was on! I have no idea how the interlock failed to turn it off. Along with its greater than 50% failure to complete cycles, shutting off halfway between treatments, with brand new batteries mind you, I've stopped using it.
I now use a CamelBak All Clear and love it. I was always afraid of dropping the SteriPen into the water while holding it and stirring it, with the CamelBak I just rotate the bottle whichever way I want to agitate the water. Re: charging via USB, if I was on a long trek, I'd have a little solar panel (Goal Zero looks interesting?), let it charge its own battery, and then plug the CamelBak into it. I'm not worried one bit about activating the lamp without it on the bottle, because I always keep it on the bottle. After the SteriPen incident, I was afraid to take it out of the pouch. Maybe the Opti has solved these issues, but I'm still hesitant.